Failsafe watercraft lift with convertible leveling system

ABSTRACT

A watercraft lift for raising and lowering a watercraft in water, including a buoyant pontoon, a lifting cradle and at least one pivot arm. The lifting cradle includes at least one air tank and a support bunk configured to receive and support the watercraft. The air tank has an internal chamber configured to receive and release pressurized air. The internal chamber has sufficient internal volume that when sufficient pressurized air is received therein the air tank has sufficient buoyancy to lift the lifting cradle to a raised position with the watercraft out of the water when positioned on the support bunk and that when sufficient pressurized air is released from the internal chamber the air tank loses sufficient buoyancy to sink the lifting cradle to a lowered position sufficiently submerged to receive and deploy the watercraft. The pivot arm is pivotally connected to the pontoon and pivotally connected to the lifting cradle to guide movement of the lifting cradle between the lowered position and the raised position.

FIELD OF THE INVENTION

The invention generally relates to an apparatus and method for lifting watercraft out of the water.

DESCRIPTION OF THE RELATED ART

The use of watercraft lifting devices is well known. Out-of-water storage prevents damage resulting from boat contact with docks, other craft or floating debris. It reduces the possibility of the boat breaking free from its moorage and floating adrift or running aground. Out-of-water storage also lessens boat damage associated with long-term exposure to water and water-based pollutants and the attachment of barnacles or other marine growth to the boat's hull. Once a boat is lifted it can be maintained in its position for extended periods of time, relieving the user of maintenance concerns. In certain situations where the water fluctuation is high, water depth is too deep, or permanent mounting is undesired, floating watercraft lifting devices are used. A number of floating lift designs are currently known that provide this basic function.

U.S. Pat. No. 5,002,000 to Rutter uses air filled pontoons as a lifting device combined with a complicated array of air inlet and outlet valves to control lateral stability while lifting. With this device the rear portion of the pontoons are lowered more than the forward portion of the pontoons to allow ingress and egress of the boat. This device, however, is limited in that the watercraft will not be raised or lowered in a horizontal position which is undesirable to many users.

U.S. Pat. No. 5,860,379 to Moody comprises of an inflatable fabric air chamber as the lifting device. While this device raises the boat out of the water, it has many disadvantages including a complicated rope tying configuration for stabilizing, non-horizontal lifting by raising the bow of the watercraft before the stern, and incompatibility with all boats by only fitting boats with outboard and inboard/outboard motors.

U.S. Pat. No. 6,848,380 to Sainz is a floating watercraft lift that addresses the fore and aft stability issues and non-horizontal lifting with the boatlifts described in Moody and Rutter by using air chambers with an arcuate longitudinal top surface and a base side that is flat. While addressing these stability issues, the lift suffers from a number of disadvantages including the lack of a means for keeping the lift stable if air pressure is lost in one or all pontoon chambers, the ability to fit in a narrow boat slip, and the lack of reserve buoyancy to keep the device from sinking if all air pressure is lost.

Two known devices, one from Hydrohoist International, Inc. and the other from Shoremaster, address the fore and aft stability and non-horizontal lifting described in Moody and Rutter in another fashion. Both devices are air displacement watercraft lifts using stabilizing brackets fixed to a dock or slip to maintain horizontal lifting of the watercraft. These fixed stabilizing brackets are undesirable for marina operations and limit the ease of portability for these lifts. A similar method for stabilizing a boat lift is described in U.S. Pat. No. 4,750,444 to Lemvig, wherein the lift is comprised of a platform with a deck and lifting skirt and link arms connecting the platform to a quay. Air is supplied to the lifting skirt to raise a watercraft while the link arms attached to the quay stabilize the platform. Similar to the Hydrohoist and Shoremaster devices, the device of Lemvig requires link arms fixed to a quay to stabilize the lift limiting the portability of the lift.

Hydrohoist International, Inc. and Airberth address portability issues with free floating side tie lifts. These lifts use air tanks rigidly attached to side floatation to control lifting and stability. While allowing for portability and side tie capabilities, these lifts do not raise the watercraft in a horizontal position and have similar disadvantages to Rutter and Moody.

In addition to the above stated short comings, the floating watercraft lifts of Rutter, Moody, Sainz, Hydrohoist, Shoremaster and Air Berth may inadvertently lower the watercraft into the water if air pressure is not maintained in one or all air chambers. In this case the watercraft will become susceptible to the damaging elements described above.

Another difficulty facing floating watercraft lift manufacturers is the multitude of mounting scenarios. To meet the lift mounting requirements, the manufacturers offer different lifts for slip, side-tie and forward mounting applications. By offering three different lifts the manufacturer and dealer must increase inventory levels and warehouse storage space.

Accordingly, there is a need in the art for a floating watercraft lift that addresses all of the following issues of horizontal lifting of the watercraft with a desirable stabilizing feature, compatibility with all boat drive configurations, stability if air pressure is lost in one or all air chambers, the ability to fit in narrow boat slips, portability for ease of installation and removal, damage tolerance to keep the watercraft out of the water if one or all of the air chambers lose air pressure, and convertibility to most floating watercraft lift mounting scenarios.

SUMMARY OF THE INVENTION

A watercraft lift for raising and lowering a watercraft in water. The watercraft lift includes a buoyant pontoon, a lifting cradle and at least one pivot arm. The lifting cradle includes at least one air tank and a support bunk configured to receive and support the watercraft. The air tank has an internal chamber configured to receive and release pressurized air. The internal chamber has sufficient internal volume that when sufficient pressurized air is received therein the air tank has sufficient buoyancy to lift the lifting cradle to a raised position with the watercraft out of the water when positioned on the support bunk and that when sufficient pressurized air is released from the internal chamber the air tank loses sufficient buoyancy to sink the lifting cradle to a lowered position sufficiently submerged to receive and deploy the watercraft. The pivot arm is pivotally connected to the pontoon and pivotally connected to the lifting cradle to guide movement of the lifting cradle between the lowered position and the raised position.

In one embodiment the pontoon includes a buoyant port pontoon portion and a buoyant starboard pontoon portion. The port and starboard pontoon portions are spaced apart sufficient to receive the watercraft therebetween.

The watercraft lift may further include ballast removably attached to the port pontoon portion and ballast removably attached to the starboard pontoon portion in amounts sufficient to prevent the watercraft lift from rolling when the watercraft is positioned on the support bunk with the watercraft lift in the raised position when all pressurized air is released from the internal chamber the air tank. The port and starboard pontoon portions are made of a first material and the ballast is made of a second material, the first material being different than the second material.

The pontoon includes a buoyant port pontoon portion having an end portion and a buoyant starboard pontoon portion having an end portion. The port and starboard pontoon portions are spaced apart sufficient to receive the watercraft therebetween. The pontoon further includes a buoyant connection pontoon portion having the end portions of the port and starboard pontoon portions attached thereto. The combined buoyancy of the port pontoon portion, the starboard pontoon portion and the connection pontoon portion is sufficient hold the watercraft out of the water when the watercraft is positioned on the support bunk with the watercraft lift in the raised position when all pressurized air is released from the internal chamber the air tank.

The port pontoon portion, the starboard pontoon portion and the connection pontoon portion have upper surfaces arranged to provide a floating dock surface for access to the watercraft from three sides thereof when positioned on the support bunk.

The connection pontoon portion has buoyant port and starboard connection pontoon portions, with the end portion of the port pontoon portion attached to the port connection pontoon portion and the end portion of the starboard pontoon portion attached to the starboard connection pontoon portion. The port connection pontoon portion and the starboard connection pontoon portion are removably attached together.

The watercraft lift may further include a lock operable to lock the pivot arm relative to the pontoon when the lifting cradle is in the raised position to prevent downward movement of the pivot arm and thereby movement of the lifting cradle to the lowered position. The lock includes a selectively rotatable upright member having an engagement member attached thereto, the rotatable member being rotatable between a locked position and an unlocked position. In the locked position the engagement member is positioned in locking engagement with the pivot arm to prevent downward movement of the pivot arm and thereby movement of the lifting cradle to the lowered position. In the unlocked position the engagement member is positioned out of locking engagement with the pivot arm to allow downward movement of the pivot arm and thereby movement of the lifting cradle to the lowered position. The lock may include a security member which when engaged prevents rotation of the rotatable member out of the locked position.

Other features and advantages of the invention will become apparent from the following detailed description, taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING(S)

The foregoing aspects and many of the attendant advantages of this invention will become more readily appreciated as the same becomes better understood by reference to the following detailed description, when taken in conjunction with the accompanying drawings, which are schematic, and not to scale, wherein:

FIG. 1 is an isometric view of a watercraft lift according to the present invention in a lowered position.

FIG. 2 is an isometric view of the watercraft lift of FIG. 1 in a position between a raised position and the lowered position.

FIG. 3 is an isometric view of the watercraft lift of FIG. 1 in the raised position.

FIG. 4 is an enlarged, isometric view of an air tank of the watercraft lift of FIG. 1.

FIG. 5 is an enlarged, isometric view of a lifting cradle of the watercraft lift of FIG. 1.

FIG. 6 is an isometric view of ballasted floating pontoons of the watercraft lift of FIG. 1.

FIG. 7 is a side view of a swing arm of the watercraft lift of FIG. 1.

FIG. 8 is an front view of the swing arm and torsion bar assembly of the watercraft lift of FIG. 1.

FIG. 9 is a sectional side elevational view of the watercraft lift of FIG. 1 showing a 4-bar linkage arrangement of the swing arms.

FIG. 10 is an enlarged, isometric view of a lock mechanism of the watercraft lift of FIG. 1.

FIG. 11 is a rear elevational view of the watercraft lift of FIG. 1 in the lowered position with the watercraft in the load/unload position.

FIG. 12 is a rear elevational view of the watercraft lift of FIG. 1 in the raised position with the watercraft in the stored position.

FIG. 13 is a top plan view of the watercraft lift of FIG. 1 in a 4-point tie configuration in a slip.

FIG. 14 is a top plan view of the watercraft lift of FIG. 1 in a forward mounting tie configuration.

FIG. 15 is a top plan view of the watercraft lift of FIG. 1 in a side tie configuration.

FIG. 16 is an isometric view of the watercraft lift of FIG. 1 with a canopy mounted to the floating pontoons.

FIG. 17 is an isometric view of the watercraft lift of FIG. 1 with a hydrodynamic element to control the acceleration and velocity of raising and lowering the lifting cradle.

FIG. 18 is an isometric view of multiple watercraft lifts of the type shown in FIG. 1 mounted side by side.

FIG. 19 is an isometric view of the watercraft lift of FIG. 1 with air hoses routed through a center of the watercraft lift.

FIG. 20 is an isometric view of the watercraft lift of FIG. 1 with the floating pontoons removed and swing arms pivotally attached to a slip.

DETAILED DESCRIPTION OF THE INVENTION

This section illustrates aspects of the invention, and points out certain preferred embodiments of these aspects. This section is not intended to be exhaustive, but rather to inform and teach the person of skill in the art who will come to appreciate more fully other aspects, equivalents, and possibilities presented by invention, and hence the scope of the invention is set forth in the claims, which alone limit its scope.

Several embodiments of the invention are set forth in the following description: FIGS. 1 through 20 provide a thorough understanding of such embodiments. One skilled in the art will understand that the present invention may be practiced without several of the details described herein. In the following description of the embodiments, it is understood that a watercraft includes any vehicle that is at least partially waterborne, which includes boats and similar vessels, but may also include amphibious vehicles including various amphibious automobiles or aircraft. Moreover, in the description that follows, it is understood that the figures related to the various embodiments are not to be interpreted as conveying any specific or relative physical dimension, and that specific or relative dimensions related to the various embodiments, if stated, are not be considered limiting unless future claims state otherwise.

An isometric view of a watercraft lift 10 in a fully lowered position is shown in FIG. 1. The watercraft lift 10, having a port side A and a starboard side B, includes a lifting cradle 50 comprising two air tanks 40 each having a lifting bunk 51, and a pair of port and starboard floating pontoons 60 with the lifting cradle positioned between the laterally spaced apart rearward portions of the floating pontoons. Fore and aft pivotal connectors 80 pivotally connect the lifting cradle 50 to the floating pontoons 60. Each pivotal connector 80 includes a torsion bar 81 extending through the lifting cradle 50 and two swing arm 70 attached to the torsion bar, one on each side of the lifting cradle. One swing arm 70 of the pivotal connector 80 is pivotally connected to the port floating pontoon 60, and the other swing arm of the pivotal connector is pivotally connected to the starboard floating pontoon 60. As best seen in FIG. 9 for the port side A, the swing arms 70 of the fore and aft pivotal connectors 80 are pivotally attached at points 91 and 92 on the port floating pontoon 60 and are also pivotally attached to the lifting cradle 50 at points 43 and 44. The lower ends of the swing arms 70 rotate forward and upwardly towards the forward floats 61 as air volume is increased within the air tanks 40. The lifting bunks 51 provide support to the hull of a watercraft 111 when in engagement therewith as shown in FIG. 12.

Again referring to FIG. 1, each floating pontoon 60 has a forward float 61, three side floats 62, side ballasts 63 and forward ballast 64. As will be described below, these floats are connected together to form a dock like structure for access to the watercraft 111 using the watercraft lift 10 from three sides.

FIG. 2 shows the watercraft lift 10 in a partially raised position from the lowered position shown in FIG. 1 which results from the pumping of air into the air tanks 40 of the lifting cradle 50 and the resulting purging of the water therein. As the air volume is increased within the air tanks 40, the lifting cradle 50 increases in buoyancy and rises to engage the lifting bunks 51 with the hull of the watercraft 111 thereabove. Thereafter, the lifting cradle 50 carries the watercraft on the lifting bunks 51 upward with the lifting cradle. If the watercraft lift 10 starts to list to the port side A, the side floats 62 on the port side A and the side ballast 63 on the starboard side B will provide the righting moment to stabilize the watercraft lift and prevent the watercraft 111 from rolling off of the lifting bunks 51. In the same manner, if the watercraft lift 10 lists to starboard side B, the side floats 62 on the starboard side B and the side ballast 63 on the port side A will provide the righting moment to stabilize the watercraft lift and prevent the watercraft 111 from rolling off of the lifting bunks 51. This provides increase laterally stability for the watercraft lift 10.

FIG. 3 shows the watercraft lift 10 in a fully raised position with the lifting cradle 50 in a raised position sufficient to hold the watercraft 111 out of the water as shown in FIG. 12. The air volume in the air tanks 40 is selected to be sufficient that in combination with the buoyancy of the floating pontoons 60 the watercraft 111 will be held in a raised position above the water (see FIG. 12). It is noted that the floating pontoons 60 stay floating in the water throughout the operation of the watercraft lift 10, and that when the lifting cradle 50 is in the fully raised position of FIG. 3 the lifting cradle and the floating pontoons are spaced apart at a first distance, and when the lifting cradle is in the fully lowered position of FIG. 1 the lifting cradle and the floating pontoons are spaced apart at a second distance with the second distance being greater than the first distance.

FIG. 4 shows an isometric view of the air tank 40 of the watercraft lift 10. The air tank 40 serves as the lower structural bar of a 4-bar linkage 90. The air tank 40 is made from a hollow rotationally molded structural plastic shell with a longitudinally extending, upwardly projecting, integrally formed strengthening rib 41, laterally extending, upwardly projecting, integrally formed forward and rearward bunk towers 48, and longitudinally extending, upwardly projecting, integrally formed gussets 47. The rib 41 provides stiffness and rigidity, and the bunk towers 48 and gussets 47 distribute the load over the entire air tank without the need for an external structure to provide the main load support and also would increase the height of the lifting cradle. The air tank 40 further has a water inlet and outlet port 45, an air inlet and outlet port 42, an adjustable relief port 46 and horizontally adjustable pivot points 43 and 44 using the adjustment brackets 49.

As shown in FIG. 5, the lifting cradle 50 has two air tanks 40, each with one lifting bunks 51 mounted to a top side thereof atop the bunk towers 48. The lifting bunks 51 is rigidly attach to the air tanks 40 on bunk towers 48 thus adding bending stiffness to the air tank of the lifting cradle 50. The lifting cradle 50 lifts the watercraft 111 by introducing air through the air inlet and outlet port 42, and thereby evacuating water within the air tank 40 through water inlet and outlet port 45, thus increasing the buoyancy of the air tank. If watercraft lift 10 lists, air will escape through the adjustable relief port 46 of the air tank 40 which is the least submerged, thus reducing its buoyancy and preventing the watercraft lift from rolling. The relief port 46 comprises a column of through-holes in the wall of the air tank, each to be at a different height relative to the water line. The relief port 46 is adjustable in that based on the size of the watercraft to be supported by the lifting cradle 50, plugs can be used to close selected ones of the through-holes and thereby control the ones which are operable. The adjustable relief port 46 is provided on the laterally outward side of each of the air tanks 40. When it is desired to lower the lifting cradle 50 to lower the watercraft 111 supported, the air within the air tanks is released through the air inlet and outlet port 42, and thereby allowing water to enter within the air tank 40 through water inlet and outlet port 45, thus decreasing the buoyancy of the air tank.

The air tanks 40 each include a longitudinally extending, laterally outward projecting lower portion 40A. As best seen in FIG. 12, the lifting cradle 50 is sized so that when positioned between the floating pontoons 60, the laterally outward projecting lower portion 40A of the port air tank 40 when the lifting cradle 50 is in the fully raised position extends laterally outward to under the lower side of the port floating pontoon and engages the lower side of the port floating pontoon, and the laterally outward projecting lower portion 40A of the starboard air tank 40 when the lifting cradle 50 is in the fully raised position extends laterally outward to under the lower side of the starboard floating pontoon and engages the lower side of the starboard floating pontoon. With this arrangement, the floating pontoons 60 serve as stops for the upward movement of the lifting cradle 50. Further, the contact of the laterally outward projecting lower portions 40A of the air tanks 40 with the lower sides of the floating pontoons 60 provides the watercraft lift 10 with increased rigidity and stability when the lifting cradle 50 is in the fully raised position shown in FIG. 12.

FIG. 6 shows the port and starboard floating pontoons 60 without the lifting cradle 50. Each of the floating pontoons 60 includes three side floats 62 and one forward float 61. The side floats 62 and the forward float 61 of each floating pontoon 60 are mechanically link together with a tube 67 to which each is attached at its laterally inward side. The side ballast 63 is removably attached to a top side of the side floats 62, and the forward ballast 64 is removably attached to a top side of the forward floats 61. The side ballast 63 includes heavy concrete tiles that provide ballast for the watercraft lift 10 as described above. The forward ballast 64 helps keep the watercraft lift 10 in an acceptable fore-aft attitude in the event air pressure within the air chambers 40 is lost or compromised and the floating pontoons 60 must support the watercraft 111 when the watercraft lift 10 is in a locked raised position which will be described below. The forward ballast 64 is shown as a heavy grate that covers a through opening in the forward float 61. The through opening reduces the light blocked by the watercraft lift 10.

The side floats 62 and the forward floats 61 are constructed of a sealed rotationally molded plastic shell with a foam filled or an air filled inner core for buoyancy. The buoyancy is selected to be sufficient to keep the watercraft 111 supported high enough above the water and in sufficient frictional contact with the lifting bunks 51 to keep the watercraft from floating off and away from the lifting cradle 50 when the lifting cradle is in the locked raised position even if all air pressure in the air tanks 40 is lost and the air tanks provide no buoyancy. The forward floats 61 are shaped on an inward side to accept and position the bow of the watercraft 111 must like a boat slip, and are designed to be used as mirrored parts as shown in FIG. 6.

The port and starboard floating pontoons 60 are attached together at a connection location 69 with a mechanical connection 68 which connects together the front floats 61 of the two floating pontoons. The floating pontoons 60 can be split at the connection location 69 and a spacer float (not shown) can be added therebetween to increase the distance between the side floats 62 of the floating pontoons to accept a boat with a wider beam.

FIG. 7 shows the swing arms 70 as having an upper pivot point 71 at an upper end thereof and a lower pivot point 72 at the opposite lower end thereof. The upper end of the swing arm 70 is pivotally attached to the floating pontoon 60 for pivotal movement relative thereto about the upper pivot point 71, and the lower end of the swing arm is rigidly attached to one end of the torsion bar 81 of the pivotal connector 80 for pivotal movement relative to the lifting cradle 50 about the lower pivot point 72. The pivotal connector 80 is shown in FIG. 8 with one of the swing arms 70 rigidly attached to each of the two opposite ends of the torsion bar 81. As shown in FIG. 7, the swing arm 70 has a substantially straight lower end portion with a shorter upper end portion at an angle relative to the lower end portion such that when the swing arm is rotated forward with the lower end shape aligned with a horizontal axis 73 with the upper pivot point 71 on the horizontal axis, the lower end portion of the of the swing arm and the lower pivot point 72 are offsets below horizontal axis.

In FIG. 9, the 4-bar linkage 90 on the port side of the watercraft lift 10 is shown as the tube 67 of the port floating pontoon 60 being a first upper bar, the air tank 40 of the lifting cradle 50 being a second lower bar, and the forward and rearward swing arms 70 of the two pivotal connectors 80 being the third and fourth bars. Of course, there is a similar 4-bar linkage 90 formed at each of the port and starboard floating pontoons 60. The upper pivot points 71 of the swing arms 70 are pivotally attached to the tube 67 of floating pontoons 60 at points 91 and 92, and the lower pivot points 72 of the swing arms are pivotally attached at points 93 and 94 to the pivots 43 and 44 of air tanks 40 by the torsion bars 81. The use of the 4-bar linkage 90 provides the watercraft lift 10 with a level lift and lowering of the watercraft 111 by the lifting cradle 50.

The adjustment brackets 49 (best seen if FIG. 4) each have an aperture through which the end portion of the torsion bar 81 extends and in which it is rotatably mounted. The adjustment brackets 49 are positionable during manufacture of the watercraft lift 10 along the rib 41 of the air tank 40 to achieve the desired longitudinal separation between the torsion bars 81 of the fore and aft pivotal connectors 80 even if the molding process used for the air tank produces a variation in the size of the air tank from one to the other.

A lock mechanism 100 is shown in FIG. 10 as being associated with one of the swing arms 70 pivotally attached to the port floating pontoon 60 and with one of the swing arms pivotally attached to the starboard floating pontoon. The lock mechanism 100 is selectively rotatable about a vertical axis to engage the adjacent swing arm 70 and limit the downward movement thereof, and thus locking the floating pontoon 60 to the lifting cradle 50 with the lifting cradle in the raised position. The lock mechanism 100 includes an engagement lever 104 at its top end, a lock shaft 101 to which the engagement lever is attached, a lock plate 103 for lock position indication, a load holding shoulder 105, and an engagement foot 102. The lock mechanism 100 is mounted through one of the side floats 62 and is bolted to the tube 67 using a clamp 106 which allows the lock shaft 101 to rotate therein relative to the side float. When the engagement lever 104 is rotated into a locked position D, the lock shaft 101 is rotate about the vertical axis to rotate the engagement foot 102 into position below the swing arm 70, thus limiting the downward rotational travel of the swing arm toward the lowered position shown in FIG. 1. When swing arm 70 rotates downward sufficient to engage the engagement foot 102, the load holding shoulder 105 transfers the load placed thereon by the swing arm and the lifting cradle 50 to which it is connected, to the side float 62 of the floating pontoon 60 through the clamp 106 and the tube 67. As discussed above, the ability to lock and hold the lifting cradle 50 in the raised position and providing the forward floats 61 and the side floats 62 of the floating pontoons 60 with sufficient buoyancy to support the full weight of the watercraft 111 and keep the watercraft above the water even should the entire air pressure in the air tanks 40 be lost, provides the watercraft lift 10 with a significant safety feature in the event of a failure that results in air pressure loss in the air tanks.

When engagement lever 104 is rotated along path E to an unlocked position C, the engagement foot 102 rotates to a position where it will not engage swing arm 70 and hence not limit downward rotation of the swing arm toward the lowered position shown in FIG. 1 and allow its unimpeded upward movement.

When the engagement lever 104 is rotated into the locked position D, the lock mechanism 100 prevents accidental or unintended lowering of the watercraft 111 into the water. Even should air pressure be released from the air tanks 40, the locking mechanism will prevent lowering of the lifting cradle 50. When the engagement lever 104 is rotated into the locked position D, the engagement lever 104 may be padlocked to the lock plate 103 or in alternative embodiments otherwise locked to prevent rotation of the lock shaft 101 and hence rotation of the engagement foot 102 from under the swing arm 70. This provides protection against theft of the watercraft 111 when on the lifting cradle 50 in the raised position since without being able to rotate the engagement lever to the unlocked position C, the lifting cradle cannot be lowered to place the watercraft in the water, thus preventing unauthorized removal of the watercraft from the watercraft lift 10.

FIG. 11 shows a rear view of the watercraft lift 10 in the lowered position with the watercraft 111 in the load/unload position. The lock mechanism 100 is in the unlocked position C. The watercraft 111 is shown floating with respect to a waterline 112 and the lifting cradle 50 is submerged below and does not touch the watercraft 111.

FIG. 12 shows a rear view of the watercraft lift 10 in the raised position with the watercraft 111 in the stored position with the lifting bunks 51 engaging the hull of the watercraft. The locking mechanism 100 is in the locked position D. The watercraft 111 rests on the lifting bunks 51 which supports it in a position above the waterline 102.

The floating pontoons 60 can be tied or attached to a dock, sea wall or quay at tie points 66. The watercraft lift 10 is shown in FIG. 13 in a 4-point tie configuration with dock lines 131 tied to a slip 132 and to the lift tie points 66 on the floating pontoons 60.

The watercraft lift 10 is shown in FIG. 14 in a forward mounting configuration with dock lines 141 tied to a dock 142 and the front lift tie points 66 on the floating pontoons 60.

The watercraft lift 10 is shown in FIG. 15 in a side tie configuration with dock lines 151 tied to a dock 152 and the lift tie points 66 on the floating pontoons 60.

The watercraft lift 10 is shown in FIG. 16 with a canopy 161 mounted to floating pontoons 60 using four canopy uprights 162.

The watercraft lift 10 is shown in FIG. 17 with a hydrodynamic brake element 171 used to control the acceleration and velocity of the raising and lowering of the lifting cradle 50. This reduces hull impact on raising of the lifting cradle 50 to provide a smooth lift. The hydrodynamic element 171 is removably attached to the lifting cradle 50 in position between the air tanks 40 and extends substantially fully between the air tanks. The hydrodynamic element 102 has a configuration selected to create increased water resistance to movement of the lifting cradle 50 as it moves upward and downward beyond the water resistance that would be experience otherwise. This is accomplished by the hydrodynamic element 102 catching the water and thereby forcing the water to flow over and around it. The hydrodynamic element 102 configuration provides water resistance that supplements the natural water resistance experienced by the lifting cradle 50 to control the acceleration and velocity of raising and lowering the lifting cradle.

A plurality of the watercraft lifts 10 are shown in FIG. 18 with the watercraft lifts mounted side-by-side. The front ends of the forward floats 61 of the floating pontoons 60 have a straight forward portion 183 that engages a straight side of a dock 181, and are mechanically connected to the dock. The adjacent outward sides 182 of the floating pontoons 60 of the watercraft lifts 10 are in engagement and the adjacent floating pontoons are mechanically connected together. In this arrangement, the watercraft lifts 10 can be used with a simple dock to provide a plurality of boat slips with floating watercraft lifts and allows the convenient construction of a marina.

The watercraft lift 10 is shown in FIG. 19 with a conduit 191 having a length centrally routed between the floating pontoons 60 and air tanks 40. The conduit 191 contains two air hoses. With this arrangement the conduit 191 and the hoses contained therein are below the watercraft 111 when on the lifting cradle 50 and hidden from view. Even when the watercraft 111 is not present, the conduit 191 provides an uncluttered appearance and reduces the chance of entanglement of the air hoses with foreign objects. The conduit 191 is corrugated and has an elastic member arranged to keep the conduit and hence the hoses out of the water and free from marine growth. The hoses within the conduit 191 connect to the air inlet and outlet port 42 of the air tanks 40 to provide pressurized air to the interior of the air tanks at sufficient pressure to evacuate the water therein and lift the lifting cradle 50 with the watercraft 111 thereon to the raised position, and to allow release of the pressurized air in the air tanks for lowering of the lifting cradle.

The watercraft lift 10 is shown in FIG. 20 with the floating pontoons 60 removed and the swing arms 70 of the pivotal connectors 80 pivotally attached to a slip 201 by their upper pivot points 71 at connection points 202, 203, 204 and 205. This arrangement allows the watercraft lift 10 to be converted from a self-supported floating lift to a lift supported by a ground supported slip as desired.

It will be appreciated that, although specific embodiments of the invention have been described herein for purposes of illustration, various modifications may be made without departing from the spirit or scope of the invention. 

1. A watercraft lift for raising and lowering a watercraft in water, comprising: a buoyant pontoon; a lifting cradle including at least one air tank and a support bunk configured to receive and support the watercraft, the air tank having an internal chamber configured to receive and release pressurized air, the internal chamber having sufficient internal volume that when sufficient pressurized air is received therein the air tank has sufficient buoyancy to lift the lifting cradle to a raised position with the watercraft out of the water when positioned on the support bunk and that when sufficient pressurized air is released from the internal chamber the air tank loses sufficient buoyancy to sink the lifting cradle to a lowered position sufficiently submerged to receive and deploy the watercraft; and at least one pivot arm pivotally connected to the pontoon and pivotally connected to the lifting cradle to guide movement of the lifting cradle between the lowered position and the raised position.
 2. The watercraft lift of claim 1 wherein the pontoon includes a buoyant port pontoon portion and a buoyant starboard pontoon portion, the port and starboard pontoon portions being spaced apart sufficient to receive the watercraft therebetween.
 3. The watercraft lift of claim 2 further including ballast positioned at the port pontoon portion and ballast positioned at the starboard pontoon portion in amounts sufficient to prevent the watercraft lift from rolling when the watercraft is positioned on the support bunk with the watercraft lift in the raised position when all pressurized air is released from the internal chamber the air tank.
 4. The watercraft lift of claim 3 wherein the ballast is removably attached to the port pontoon portion and the ballast is removably attached to the starboard pontoon portion.
 5. The watercraft lift of claim 3 wherein the port and starboard pontoon portions are made of a first material and the ballast is made of a second material, the first material being different than the second material.
 6. The watercraft lift of claim 1 wherein the pontoon includes a buoyant port pontoon portion having an end portion and a buoyant starboard pontoon portion having an end portion, the port and starboard pontoon portions being spaced apart sufficient to receive the watercraft therebetween, and further includes a buoyant connection pontoon portion having the end portions of the port and starboard pontoon portions attached thereto, the combined buoyancy of the port pontoon portion, the starboard pontoon portion and the connection pontoon portion being sufficient the support bunk in sufficient contact with the watercraft to prevent the watercraft from floating off of the support bunk when the watercraft is positioned on the support bunk with the watercraft lift in the raised position when all pressurized air is released from the internal chamber the air tank.
 7. The watercraft lift of claim 1 wherein the pontoon includes a buoyant port pontoon portion having an end portion and a buoyant starboard pontoon portion having an end portion, the port and starboard pontoon portions being spaced apart sufficient to receive the watercraft therebetween, and further includes a buoyant connection pontoon portion having the end portions of the port and starboard pontoon portions attached thereto, the port pontoon portion, the starboard pontoon portion and the connection pontoon portion having upper surfaces arranged to provide a floating dock surface for access to the watercraft from three sides thereof when positioned on the support bunk.
 8. The watercraft lift of claim 1 wherein the pontoon includes a buoyant port pontoon portion having an end portion and a buoyant starboard pontoon portion having an end portion, the port and starboard pontoon portions being spaced apart sufficient to receive the watercraft therebetween, and further includes buoyant port and starboard connection pontoon portions, the end portion of the port pontoon portion being attached to the port connection pontoon portion and the end portion of the starboard pontoon portion being attached to the starboard connection pontoon portion, and the port connection pontoon portion and the starboard connection pontoon portion being removably attached together.
 9. The watercraft lift of claim 1 further including a lock operable to lock the pivot arm relative to the pontoon when the lifting cradle is in the raised position to prevent downward movement of the pivot arm and thereby movement of the lifting cradle to the lowered position.
 10. The watercraft lift of claim 9 wherein the lock includes a selectively rotatable upright member having an engagement member attached thereto, the rotatable member being rotatable between a locked position and an unlocked position, in the locked position the engagement member being positioned in locking engagement with the pivot arm to prevent downward movement of the pivot arm and thereby movement of the lifting cradle to the lowered position, and in the unlocked position the engagement member being positioned out of locking engagement with the pivot arm to allow downward movement of the pivot arm and thereby movement of the lifting cradle to the lowered position.
 11. The watercraft lift of claim 10 wherein the lock includes a security member which when engaged prevents rotation of the rotatable member out of the locked position.
 12. The watercraft lift of claim 1 wherein the pivot arm has an upper end portion pivotally connected to the pontoon and a lower end portion pivotally connected to the air tank of the lifting cradle using a laterally extending member, the lower end portion of the pivot arm being connected to an end portion of the member to provide a pivotal connection between the lower end portion of the pivot arm and the air tank.
 13. The watercraft lift of claim 1 wherein the air tank has a longitudinally extending integrally molded structural rib projecting upward, the member extending laterally through the structural rib.
 14. The watercraft lift of claim 1 wherein the at least one pivot arm includes first and second spaced apart port pivot arms, each having an upper end portion pivotally connected to the pontoon and a lower end portion pivotally connected to the lifting cradle, and wherein the air tank has a longitudinally extending integrally molded structural rib projecting upward and the lower end portions of the first and second pivot arms are pivotally connected to the structural rib.
 15. The watercraft lift of claim 14 wherein the support bunk is attached to the air tank in a manner to provide longitudinal rigidity to the air tank.
 16. The watercraft lift of claim 1 wherein the air tank has a laterally projecting portion extending outward to under the pontoon to engage the pontoon upon the lifting cradle reaching the raised position.
 17. A watercraft lift for raising and lowering a watercraft in water, comprising: a buoyant pontoon having a buoyant port pontoon portion with an end portion, a buoyant starboard pontoon portion with an end portion, and a buoyant connection pontoon portion with the end portions of the port and starboard pontoon portions attached thereto, the port and starboard pontoon portions being spaced apart sufficient to receive the watercraft therebetween; a lifting cradle including an air tank assembly and a support bunk configured to receive and support the watercraft, the air tank assembly having at least one internal chamber configured to receive and release pressurized air, the internal chamber having sufficient internal volume that when sufficient pressurized air is received therein the air tank assembly has sufficient buoyancy to lift the lifting cradle to a raised position with the watercraft out of the water when positioned on the support bunk and that when sufficient pressurized air is released from the internal chamber the air tank assembly loses sufficient buoyancy to sink the lifting cradle to a lowered position sufficiently submerged to receive and deploy the watercraft; and at least one port pivot arm pivotally connected to the port pontoon portion and pivotally connected to the lifting cradle, and at least one starboard pivot arm pivotally connected to the starboard pontoon portion and pivotally connected to the lifting cradle, the port and starboard pivot arms configured to guide movement of the lifting cradle between the lowered position and the raised position.
 18. The watercraft lift of claim 17 wherein the port and starboard pivot arms are pivotally connected to the lifting cradle using a member extending between a port side of the lifting cradle and a starboard side of the lifting cradle, the port pivot arm being connected to a port end of the member and the starboard pivot arm being connected to a starboard end of the member.
 19. The watercraft lift of claim 18 wherein the member is a torsion bar.
 20. The watercraft lift of claim 17 wherein the pontoon includes a buoyant port pontoon portion having an end portion and a buoyant starboard pontoon portion having an end portion, the port and starboard pontoon portions being spaced apart sufficient to receive the watercraft therebetween, and further includes a buoyant connection pontoon portion having the end portions of the port and starboard pontoon portions attached thereto, the combined buoyancy of the port pontoon portion, the starboard pontoon portion and the connection pontoon portion being sufficient the support bunk in sufficient contact with the watercraft to prevent the watercraft from floating off of the support bunk when the watercraft is positioned on the support bunk with the watercraft lift in the raised position when all pressurized air is released from the internal chamber the air tank assembly.
 21. The watercraft lift of claim 17 further including a first lock operable to lock the port pivot arm relative to the port pontoon portion when the lifting cradle is in the raised position to prevent downward movement of the port pivot arm and thereby movement of the lifting cradle to the lowered position, and a second lock operable to lock the starboard pivot arm relative to the starboard pontoon portion when the lifting cradle is in the raised position to prevent downward movement of the starboard pivot arm and thereby movement of the lifting cradle to the lowered position.
 22. The watercraft lift of claim 21 wherein the first lock includes a selectively rotatable first rotatable upright member having a first engagement member attached thereto, the first rotatable member being rotatable supported by the port pontoon portion and rotatable between a locked position and an unlocked position, in the locked position the first engagement member being positioned in locking engagement with the port pivot arm to prevent downward movement of the port pivot arm and thereby movement of the lifting cradle to the lowered position, and in the unlocked position the engagement member being positioned out of locking engagement with the port pivot arm to allow downward movement of the port pivot arm and thereby movement of the lifting cradle to the lowered position, and a selectively rotatable second rotatable upright member having a second engagement member attached thereto, the second rotatable member being rotatable supported by the starboard pontoon portion and rotatable between a locked position and an unlocked position, in the locked position the second engagement member being positioned in locking engagement with the starboard pivot arm to prevent downward movement of the starboard pivot arm and thereby movement of the lifting cradle to the lowered position, and in the unlocked position the engagement member being positioned out of locking engagement with the starboard pivot arm to allow downward movement of the starboard pivot arm and thereby movement of the lifting cradle to the lowered position.
 23. The watercraft lift of claim 22 wherein the first lock includes a first security member which when engaged prevents rotation of the first rotatable member out of the locked position, and the second lock includes a second security member when engaged prevents rotation of the second rotatable member out of the locked position.
 24. The watercraft lift of claim 17 wherein the port and starboard pivot arms each have an upper end portion and a lower end portion, the upper end portion of the port pivot arm being pivotally connected to the port pontoon portion and the lower end portion of the port pivot arm being pivotally connected to the air tank assembly of the lifting cradle, and the upper end portion of the starboard pivot arm being pivotally connected to the starboard pontoon portion and the lower end portion of the starboard pivot arm being pivotally connected to the air tank assembly of the lifting cradle.
 25. The watercraft lift of claim 24 further including a member extending between a port side of the air tank assembly and a starboard side of the air tank assembly, the lower end portion of the port pivot arm being connected to a port end of the member and the lower end portion of the starboard pivot arm being connected to a starboard end of the member.
 26. The watercraft lift of claim 17 wherein the air tank assembly has a longitudinally extending integrally molded structural rib projecting upward, the member extending laterally through the structural rib.
 27. The watercraft lift of claim 17 wherein the at least one port pivot arm includes first and second spaced apart port pivot arms, each having an upper end portion pivotally connected to the port pontoon portion and a lower end portion pivotally connected to the lifting cradle, and the at least one starboard pivot arm includes first and second spaced apart starboard pivot arms, each having an upper end portion pivotally connected to the starboard pontoon portion and a lower end portion pivotally connected to the lifting cradle, and wherein the air tank assembly has a longitudinally extending integrally molded structural rib projecting upward and the lower end portions of the first and second port and starboard pivot arms are pivotally connected to the structural rib.
 28. The watercraft lift of claim 27 wherein the support bunk is attached to the air tank assembly in a manner to provide longitudinal rigidity to the air tank assembly.
 29. The watercraft lift of claim 17 wherein the air tank has a laterally projecting portion extending outward to under the pontoon to engage the pontoon upon the lifting cradle reaching the raised position.
 30. A watercraft lift for raising and lowering a watercraft in water, comprising: a buoyant pontoon having a buoyant port pontoon portion with an end portion, a buoyant starboard pontoon portion with an end portion, and a buoyant connection pontoon portion with the end portions of the port and starboard pontoon portions attached thereto, the port and starboard pontoon portions being spaced apart sufficient to receive the watercraft therebetween; a lifting cradle with support bunks attached thereto and including a port internal chamber configured to receive and release pressurized air, and a starboard internal chamber configured to receive and release pressurized air, the support bunks being configured to receive and support the watercraft, the combined port and starboard internal chambers having sufficient internal volume that when sufficient pressurized air is received therein the lifting cradle has sufficient buoyancy to lift the lifting cradle to a raised position with the watercraft out of the water when positioned on the support bunks and that when sufficient pressurized air is released from the port and starboard internal chambers the lifting cradle loses sufficient buoyancy to sink the lifting cradle to a lowered position sufficiently submerged to receive and deploy the watercraft; and at least one port pivot arm having an upper end portion pivotally connected to the port pontoon portion and a lower end portion pivotally connected to the lifting cradle, and at least one starboard pivot arm having an upper end portion pivotally connected to the starboard pontoon portion and a lower end portion pivotally connected to the lifting cradle, the port and starboard pivot arms configured to guide movement of the lifting cradle between the lowered position and the raised position.
 31. The watercraft lift of claim 30 wherein a lifting cradle includes at least one port air tank defining the port internal chamber and at least one starboard air tank defining the starboard internal chamber.
 32. The watercraft lift of claim 31 further including a hydrodynamic brake extending between the port and starboard air tanks to create additional resistance against movement of the lifting cradle.
 33. The watercraft lift of claim 31 wherein the lower end portion of the port pivot arm is pivotally connected to the port air tank of the lifting cradle, and the lower end portion of the starboard pivot arm is pivotally connected to the starboard air tank of the lifting cradle.
 34. The watercraft lift of claim 33 wherein the lower end portions of the port and starboard pivot arms are pivotally connected to the port and starboard air tanks of the lifting cradle using a member extending between a port side of the port air tank and a starboard side of the starboard air tank, the lower end portion of the port pivot arm being connected to a port end of the member and the lower end portion of the starboard pivot arm being connected to a starboard end of the member.
 35. The watercraft lift of claim 34 wherein the member is a torsion bar extending through an aperture in the port and starboard air tanks.
 36. The watercraft lift of claim 31 wherein the port air tank has a laterally projecting portion extending outward to under the port pontoon portion to engage the port pontoon portion upon the lifting cradle reaching the raised position, and the starboard air tank has a laterally projecting portion extending outward to under the starboard pontoon portion to engage the starboard pontoon portion upon the lifting cradle reaching the raised position.
 37. The watercraft lift of claim 30 further including a port relief port communicating with the port internal chamber and a starboard relief port communicating with the starboard internal chamber, the port and starboard relief ports being arranged to permit the release of pressurized air in one of the port internal chamber and the starboard internal chamber based on which is least submerged in the water.
 38. The watercraft lift of claim 37 wherein a lifting cradle includes at least one port air tank defining the port internal chamber and at least one starboard air tank defining the starboard internal chamber, and the port relief port is positioned at a port side of the port air tank and the starboard relief port is positioned at a starboard side of the starboard air tank.
 39. The watercraft lift of claim 30 further including a hydrodynamic brake extending between the port and starboard air tanks to create additional resistance against movement of the lifting cradle.
 40. The watercraft lift of claim 30 for conversion for use with a slip having port and starboard side members, wherein the upper end portion of the port pivot arm is removably connected to the port pontoon portion and pivotally attachable to the port side member of the slip, and the upper end portion of the starboard pivot arm is removably connected to the starboard pontoon portion and pivotally attachable to the starboard side member of the slip.
 41. The watercraft lift of claim 30 wherein the port and starboard pontoon portions are each a rotomolded plastic part.
 42. A watercraft lift for raising and lowering a watercraft in water, comprising: a buoyant pontoon having a buoyant port pontoon portion with an end portion, a buoyant starboard pontoon portion with an end portion, and a buoyant connection pontoon portion with the end portions of the port and starboard pontoon portions attached thereto, the port and starboard pontoon portions being spaced apart sufficient to receive the watercraft therebetween; a lifting cradle including a port air tank with a port support bunk attached thereto and having an internal chamber configured to receive and release pressurized air, and a starboard air tank with a starboard support bunk attached thereto and having an internal chamber configured to receive and release pressurized air, the port and starboard support bunks being configured to receive and support the watercraft, the combined internal chambers of the port and starboard air tanks having sufficient internal volume that when sufficient pressurized air is received therein the port and starboard air tanks have sufficient buoyancy to lift the lifting cradle to a raised position with the watercraft out of the water when positioned on the port and starboard support bunks and that when sufficient pressurized air is released from the internal chambers of the port and starboard air tanks the air tanks loses sufficient buoyancy to sink the lifting cradle to a lowered position sufficiently submerged to receive and deploy the watercraft; and first and second spaced apart port pivot arms, each having an upper end portion pivotally connected to the port pontoon portion and a lower end portion pivotally connected to the lifting cradle, and first and second spaced apart starboard pivot arms, each having an upper end portion pivotally connected to the starboard pontoon portion and a lower end portion pivotally connected to the lifting cradle, the port and starboard pivot arms configured to guide movement of the lifting cradle between the lowered position and the raised position, the first and second port pivot arms, the port pontoon portion and the lifting cradle being in a 4-bar linkage arrangement and the first and second starboard pivot arms, the starboard pontoon portion and the lifting cradle being in a 4-bar linkage arrangement.
 43. The watercraft lift of claim 42 wherein the lower end portions of the first and second port pivot arms are pivotally connected to the port air tank of the lifting cradle, and the lower end portions of the first and second of the starboard pivot arms are pivotally connected to the starboard air tank of the lifting cradle.
 44. The watercraft lift of claim 43 wherein the lower end portions of the first port pivot arm and the first starboard pivot arm are pivotally connected to the port and starboard air tanks of the lifting cradle using a first member extending between a port side of the port air tank and a starboard side of the starboard air tank, the lower end portion of the first port pivot arm being connected to a port end of the first member and the lower end portion of the first starboard pivot arm being connected to a starboard end of the first member, and wherein the lower end portions of the second port pivot arm and the second starboard pivot arm are pivotally connected to the port and starboard air tanks of the lifting cradle using a second member extending between a port side of the port air tank and a starboard side of the starboard air tank and spaced apart from the first member, the lower end portion of the second port pivot arm being connected to a port end of the second member and the lower end portion of the second starboard pivot arm being connected to a starboard end of the second member.
 45. The watercraft lift of claim 44 wherein the first and second member are a torsion bars, each extending through an aperture in the port and starboard air tanks.
 46. The watercraft lift of claim 44 wherein the port and starboard air tanks each have a longitudinally extending integrally molded structural rib projecting upward, the first member extending through the structural rib of the port and starboard air tanks, and the second member extending through the structural rib of the port and starboard air tanks.
 47. The watercraft lift of claim 43 wherein the port and starboard air tanks each have a longitudinally extending integrally molded structural rib projecting upward, and the lower end portions of the first and second port pivot arms are pivotally connected to the structural rib of the port air tank and the lower end portions of the first and second starboard pivot arms are pivotally connected to the structural rib of the starboard air tank.
 48. The watercraft lift of claim 47 wherein the port support bunk is attached to the port air tank in a manner to provide longitudinal rigidity to the port air tank, and the starboard support bunk is attached to the starboard air tank in a manner to provide longitudinal rigidity to the starboard air tank.
 49. The watercraft lift of claim 42 further including a port relief port communicating with the interior chamber of the port air tank and a starboard relief port communicating with the interior chamber of the starboard air tank, the port and starboard relief ports being arranged to permit the release of pressurized air in the interior chamber of the one of the port and starboard air tanks that is least submerged in the water.
 50. The watercraft lift of claim 49 wherein the port relief port is positioned at the port side of the port air tank and the starboard relief port is positioned at the starboard side of the starboard air tank.
 51. The watercraft lift of claim 42 further including a first lock operable to lock one of the first and second port pivot arms relative to the port pontoon portion when the lifting cradle is in the raised position to prevent downward movement of the one port pivot arm and thereby movement of the lifting cradle to the lowered position, and a second lock operable to lock one of the first and second starboard pivot arms relative to the starboard pontoon portion when the lifting cradle is in the raised position to prevent downward movement of the one starboard pivot arm and thereby movement of the lifting cradle to the lowered position.
 52. The watercraft lift of claim 51 wherein the first lock includes a selectively rotatable first rotatable upright member having a first engagement member attached thereto, the first rotatable member being rotatable supported by the port pontoon portion and rotatable between a locked position and an unlocked position, in the locked position the first engagement member being positioned in locking engagement with the one port pivot arm to prevent downward movement of the one port pivot arm and thereby movement of the lifting cradle to the lowered position, and in the unlocked position the engagement member being positioned out of locking engagement with the one port pivot arm to allow downward movement of the one port pivot arm and thereby movement of the lifting cradle to the lowered position, and a selectively rotatable second rotatable upright member having a second engagement member attached thereto, the second rotatable member being rotatable supported by the starboard pontoon portion and rotatable between a locked position and an unlocked position, in the locked position the second engagement member being positioned in locking engagement with the one starboard pivot arm to prevent downward movement of the one starboard pivot arm and thereby movement of the lifting cradle to the lowered position, and in the unlocked position the engagement member being positioned out of locking engagement with the one starboard pivot arm to allow downward movement of the one starboard pivot arm and thereby movement of the lifting cradle to the lowered position.
 53. The watercraft lift of claim 52 wherein the first lock includes a first security member which when engaged prevents rotation of the first rotatable member out of the locked position, and the second lock includes a second security member when engaged prevents rotation of the second rotatable member out of the locked position.
 54. A watercraft lift for raising and lowering a watercraft in water, attachable to a slip having a port side and a starboard side, the watercraft lift comprising: a lifting cradle including a port air tank with a port support bunk attached thereto and having an internal chamber configured to receive and release pressurized air, and a starboard air tank with a starboard support bunk attached thereto and having an internal chamber configured to receive and release pressurized air, the port and starboard support bunks being configured to receive and support the watercraft, the combined internal chambers of the port and starboard air tanks having sufficient internal volume that when sufficient pressurized air is received therein the port and starboard air tanks have sufficient buoyancy to lift the lifting cradle to a raised position with the watercraft out of the water when positioned on the port and starboard support bunks and that when sufficient pressurized air is released from the internal chambers of the port and starboard air tanks the air tanks loses sufficient buoyancy to sink the lifting cradle to a lowered position sufficiently submerged to receive and deploy the watercraft; first and second spaced apart port pivot arms, each having an upper end portion pivotally connectable to the port side of the slip and a lower end portion pivotally connected to the lifting cradle, and first and second spaced apart starboard pivot arms, each having an upper end portion pivotally connectable to the starboard side of the slip and a lower end portion pivotally connected to the lifting cradle, the port and starboard pivot arms configured to guide movement of the lifting cradle between the lowered position and the raised position, the first and second port pivot arms, the port side of the slip and the lifting cradle forming a 4-bar linkage arrangement and the first and second starboard pivot arms, the starboard side of the slip and the lifting cradle forming a 4-bar linkage arrangement; and a first lock operable to lock one of the first and second port pivot arms relative to the port side of the slip when the lifting cradle is in the raised position to prevent downward movement of the one port pivot arm and thereby movement of the lifting cradle to the lowered position, and a second lock operable to lock one of the first and second starboard pivot arms relative to the starboard side of the slip when the lifting cradle is in the raised position to prevent downward movement of the one starboard pivot arm and thereby movement of the lifting cradle to the lowered position.
 55. The watercraft lift of claim 54 wherein the first lock includes a selectively rotatable first rotatable upright member having a first engagement member attached thereto, the first rotatable member being rotatable supported by the port side of the slip and rotatable between a locked position and an unlocked position, in the locked position the first engagement member being positioned in locking engagement with the one port pivot arm to prevent downward movement of the one port pivot arm and thereby movement of the lifting cradle to the lowered position, and in the unlocked position the engagement member being positioned out of locking engagement with the one port pivot arm to allow downward movement of the one port pivot arm and thereby movement of the lifting cradle to the lowered position, and a selectively rotatable second rotatable upright member having a second engagement member attached thereto, the second rotatable member being rotatable supported by the starboard side of the slip and rotatable between a locked position and an unlocked position, in the locked position the second engagement member being positioned in locking engagement with the one starboard pivot arm to prevent downward movement of the one starboard pivot arm and thereby movement of the lifting cradle to the lowered position, and in the unlocked position the engagement member being positioned out of locking engagement with the one starboard pivot arm to allow downward movement of the one starboard pivot arm and thereby movement of the lifting cradle to the lowered position.
 56. The watercraft lift of claim 55 wherein the first lock includes a first security member which when engaged prevents rotation of the first rotatable member out of the locked position, and the second lock includes a second security member when engaged prevents rotation of the second rotatable member out of the locked position.
 57. A watercraft lift for raising and lowering a watercraft in water, attachable to a slip having a port side and a starboard side, the watercraft lift comprising: a lifting cradle including a port air tank with a port support bunk attached thereto and having an internal chamber configured to receive and release pressurized air, and a starboard air tank with a starboard support bunk attached thereto and having an internal chamber configured to receive and release pressurized air, the port and starboard support bunks being configured to receive and support the watercraft, the combined internal chambers of the port and starboard air tanks having sufficient internal volume that when sufficient pressurized air is received therein the port and starboard air tanks have sufficient buoyancy to lift the lifting cradle to a raised position with the watercraft out of the water when positioned on the port and starboard support bunks and that when sufficient pressurized air is released from the internal chambers of the port and starboard air tanks the air tanks loses sufficient buoyancy to sink the lifting cradle to a lowered position sufficiently submerged to receive and deploy the watercraft; first and second spaced apart port pivot arms, each having an upper end portion pivotally connectable to the port side of the slip and a lower end portion pivotally connected to the lifting cradle, and first and second spaced apart starboard pivot arms, each having an upper end portion pivotally connectable to the starboard side of the slip and a lower end portion pivotally connected to the lifting cradle, the port and starboard pivot arms configured to guide movement of the lifting cradle between the lowered position and the raised position, the first and second port pivot arms, the port side of the slip and the lifting cradle forming a 4-bar linkage arrangement and the first and second starboard pivot arms, the starboard side of the slip and the lifting cradle forming a 4-bar linkage arrangement; and a first member attached to port and starboard air tanks and extending between a port side of the port air tank and a starboard side of the starboard air tank, the lower end portions of the first port pivot arm and the first starboard pivot arm being pivotally connected to the port and starboard air tanks of the lifting cradle using the first member, the lower end portion of the first port pivot arm being connected to a port end of the first member and the lower end portion of the first starboard pivot arm being connected to a starboard end of the first member; and a second member attached to port and starboard air tanks and extending between a port side of the port air tank and a starboard side of the starboard air tank and spaced apart from the first member, the lower end portions of the second port pivot arm and the second starboard pivot arm being pivotally connected to the port and starboard air tanks of the lifting cradle using the second member, the lower end portion of the second port pivot arm being connected to a port end of the second member and the lower end portion of the second starboard pivot arm being connected to a starboard end of the second member.
 58. The watercraft lift of claim 57 wherein the first and second member are a torsion bars, each extending through an aperture in the port and starboard air tanks.
 59. The watercraft lift of claim 57 wherein the port and starboard air tanks each have a longitudinally extending integrally molded structural rib projecting upward, the first member extending through the structural rib of the port and starboard air tanks, and the second member extending through the structural rib of the port and starboard air tanks.
 60. The watercraft lift of claim 57 wherein the port support bunk is attached to the port air tank in a manner to provide longitudinal rigidity to the port air tank, and the starboard support bunk is attached to the starboard air tank in a manner to provide longitudinal rigidity to the starboard air tank.
 61. A watercraft lift for raising and lowering a watercraft in water, attachable to a slip having a port side and a starboard side, the watercraft lift comprising: a lifting cradle including a port air tank with a port support bunk attached thereto and having an internal chamber configured to receive and release pressurized air, and a starboard air tank with a starboard support bunk attached thereto and having an internal chamber configured to receive and release pressurized air, the port and starboard support bunks being configured to receive and support the watercraft, the combined internal chambers of the port and starboard air tanks having sufficient internal volume that when sufficient pressurized air is received therein the port and starboard air tanks have sufficient buoyancy to lift the lifting cradle to a raised position with the watercraft out of the water when positioned on the port and starboard support bunks and that when sufficient pressurized air is released from the internal chambers of the port and starboard air tanks the air tanks loses sufficient buoyancy to sink the lifting cradle to a lowered position sufficiently submerged to receive and deploy the watercraft; first and second spaced apart port pivot arms, each having an upper end portion pivotally connectable to the port side of the slip and a lower end portion pivotally connected to the lifting cradle, and first and second spaced apart starboard pivot arms, each having an upper end portion pivotally connectable to the starboard side of the slip and a lower end portion pivotally connected to the lifting cradle, the port and starboard pivot arms configured to guide movement of the lifting cradle between the lowered position and the raised position, the first and second port pivot arms, the port side of the slip and the lifting cradle forming a 4-bar linkage arrangement and the first and second starboard pivot arms, the starboard side of the slip and the lifting cradle forming a 4-bar linkage arrangement; and a hydrodynamic brake extending between the port and starboard air tanks to create additional resistance against movement of the lifting cradle. 